Q: "Does the Church of Jesus Christ of Latter-day Saints recognize that the word testament as mentioned in the titles "Old Testament/New Testament" refer to an old and new covenant? Likewise since Hebrews wrote the entire OT/NT and the Book of Mormon is believed to be written by the lost tribes of Hebrews, or some sort of mixed generations (apologies still trying to learn more). That the inhabitants of the land "Bountiful" would intend that "Another Testament of Jesus Christ" would simply mean another covenant?"

 A: Thank you for your thoughtful question.

The word "testament" does not mean covenant.  It means: witness, testimony, statement, proof, or attestation. So, the phrase "Another Testament of Jesus Christ" means "another witness" or "another testimony" of Jesus Christ.

We believe that the full gospel of Jesus Christ was given to Adam from the very beginning and was passed down and revealed throughout the generations of the patriarchs. It was this gospel that Moses received on the mount. However, when the Children of Israel rebelled and rejected this gospel, they were given a lesser law, one that would prepare them to again receive the fullness of the Gospel of Christ one day. This lesser law is referred to as the "Law of Moses" and was administered by the Aaronic Priesthood. It included the strict laws of purification, animal sacrifices, food restrictions, etc. The Book of Mormon explains:
29 And now I say unto you that it was expedient that there should be a law given to the children of Israel, yea, even a very strict law; for they were a stiffnecked people, quick to do iniquity, and slow to remember the Lord their God;
30 Therefore there was a law given them, yea, a law of performances and of ordinances, a law which they were to observe strictly from day to day, to keep them in remembrance of God and their duty towards him.
31 But behold, I say unto you, that all these things were types of things to come.
32 And now, did they understand the law? I say unto you, Nay, they did not all understand the law; and this because of the hardness of their hearts; for they understood not that there could not any man be saved except it were through the redemption of God. (Mosiah 13:29-32)
Book of Mormon prophets before the coming of Christ understood that they were obliged to obey the Law of Moses, but that when Christ came, it would have an end. The prophet Abinadi explained:
27 And now ye have said that salvation cometh by the law of Moses. I say unto you that it is expedient that ye should keep the law of Moses as yet; but I say unto you, that the time shall come when it shall no more be expedient to keep the law of Moses.
28 And moreover, I say unto you, that salvation doth not come by the law alone; and were it not for the atonement, which God himself shall make for the sins and iniquities of his people, that they must unavoidably perish, notwithstanding the law of Moses. (Mosiah 13:27-28)
The Law of Moses was in effect from the time of Moses until Jesus Christ completed his ministry. After His resurrection, the Law was fulfilled and was replaced by the fullness of the Gospel of Jesus Christ which was preached by Peter, Paul, James and the other apostles.

It's important to understand that even though the Law of Moses was fulfilled, it does not negate the prophesies and promises that are recorded in the Old Testament. Jesus and the apostles in the New Testament referred to many Old Testament prophesies and stated that they must all be fulfilled. When Jesus appeared on the American Continent as recorded in the Book of Mormon, he explained:
2 And it came to pass that when Jesus had said these words he perceived that there were some among them who marveled, and wondered what he would concerning the law of Moses; for they understood not the saying that old things had passed away, and that all things had become new.
3 And he said unto them: Marvel not that I said unto you that old things had passed away, and that all things had become new.
4 Behold, I say unto you that the law is fulfilled that was given unto Moses.
5 Behold, I am he that gave the law, and I am he who covenanted with my people Israel; therefore, the law in me is fulfilled, for I have come to fulfil the law; therefore it hath an end.
6 Behold, I do not destroy the prophets, for as many as have not been fulfilled in me, verily I say unto you, shall all be fulfilled.
7 And because I said unto you that old things have passed away, I do not destroy that which hath been spoken concerning things which are to come.
8 For behold, the covenant which I have made with my people is not all fulfilled; but the law which was given unto Moses hath an end in me. (3 Nephi 15:2-8)
Because the Old Testament includes the Law of Moses and the New Testament preaches the Gospel of Jesus Christ, some faith traditions have chosen, as a matter of simplicity and convenience, to refer to the Old Testament as the "old covenant" and the New Testament as the "new covenant." This can lead to confusion, however, because there are many prophesies and promises contained in the Old Testament (such as the prophesies of Isaiah, for example) which are still in force and can be instructive. In addition, referring to the Old Testament as the "old covenant" gives the wrong impression that such prophets as Adam, Abraham, Joseph, Isaiah, and others did not have or understand the full gospel. They did.